1. Field of the Invention
The present invention relates to a direct-heated flat emitter for creating an electron beam, particularly for x-ray tubes, with two terminal lugs formed at the edge of the perimeter for the heat supply.
2. Description of the Prior Art
For mammography there are x-ray tubes with rectangular surface emitters consisting of tungsten sheet that is about 50 .mu.m thick. These flat emitters are provided with mutually parallel slits proceeding in alternating fashion from mutually opposite sides, so that interconnects are formed which produce a serpentine current path that enables a direct heating of the flat emitter.
Flat emitters are also known from French Patent 58 949, French Patent 978 627, British Specification 10 11 398, German OS 37 17 974 and German PS 39 01 337.
Such emitters share the problem that an electron beam having an optimally homogenous electron distribution over its cross-section can only be generated if the slits are very narrow. The slits cannot be made arbitrarily narrow, however, there is the danger of shorts between neighboring interconnects. Besides this, there is the danger of voltage arcing between neighboring interconnects. Both lead to a shortening of the lifetime of the flat emitter or even to its premature failure.